Abstract:
We propose an upgrade of Advanced LIGO (aLIGO), named LIGO-LF, that focuses
on improving the sensitivity in the 5-30 Hz low-frequency band, and we explore
the upgrade's astrophysical applications. We present a comprehensive study of
the detector's technical noises, and show that with the new technologies such
as interferometrically-sensed seismometers and balanced-homodyne readout,
LIGO-LF can reach the fundamental limits set by quantum and thermal noises down
to 5 Hz. These technologies are also directly applicable to the future
generation of detectors. LIGO-LF can observe a rich array of astrophysical
sources such as binary black holes with total mass up to 2000 M_\odot. The
horizon distance of a single LIGO-LF detector will be z ~ 6, greatly exceeding
aLIGO's reach. Additionally, for a given source the chirp mass and total mass
can be constrained 2 times better, and the effective spin 3-5 times better,
than aLIGO. The total number of detected merging black holes will increase by a
factor of 16 compared with aLIGO. Meanwhile, LIGO-LF will also significantly
enhance the probability of detecting other astrophysical phenomena including
the gravitational memory effects and the neutron star r-mode resonances.